1. Field of the Invention
This invention relates generally to gas-fired hot air furnaces, and more particularly to a condensing mode furnace of that type.
2. Description of the Prior Art
Atmospheric-type, gas fired hot air furnaces conventionally comprise a gas burner in the form of a gas jet firing into a combustion chamber, combustion air being supplied at atmospheric pressure; a heat exchanger for extracting heat from the products of combustion of the burner; an exhaust passage for carrying the products of combustion from the heat exchanger to an exhaust flue; an air passage for carrying a flow of air over the heat exchanger to a hot air outlet thereby to extract heat from the heat exchanger; and a blower for causing a flow of air through the air passage.
Condensing mode furnaces are known which include a condenser for condensing water out of the products of combustion to reduce the stack temperature and thereby increase the efficiency of the furnace.
Conventional atmospheric-type, gas-fired hot air furnace systems typically include a thermostat for sensing the temperature in the space to be heated, and a furnace control including a fan and limit switch. Closing of the thermostat contacts causes opening of a solenoid-operated gas valve, ignition of the gas being provided by a pilot or spark ignition, followed by initiation of operation of the blower by the fan switch. Opening of the thermostat contacts causes closing of the gas valve and the fan switch thereafter terminates operation of the blower.